It was a pretty common issue in Unreal and I overlooked it—silly me:
The issue was caused by an Instance Override on the Character Actor placed in the level. Because the level instance wasn’t synced with the Blueprint’s Class Defaults, the Map inside the instance was holding outdated/empty struct data, causing Get Instanced Struct Value to return Not Valid.
Fix:
I selected the Actor Component on the placed Character in the scene, clicked the “Reset to Default” (white arrow) next to the Map variable in the Details panel to pull the updated Class Defaults, and recompiled.
I hope this helps someone in the future.
